This invention relates generally to a device or gun for painting powder particles, and more particularly to a device for painting powder particles by triboelectrification spraying.
Conventionally known are various types of devices for painting by electrostatic powder spraying, wherein, in general, a corona discharge is utilized for electrifying powder particles so as to electrostatically adhere said powder particles to a surface to be coated. According to this corona discharge device, a high electric voltage is applied to corona pins arranged so as to generate ions, powder particles are electrified by means of the corona ions thus generated, and at the same time the electrified powder particles are sprayed so as to adhere to the surface to be coated.
A typical conventionally known spray gun of this type is illustrated in FIG. 3. In this gun, spray powder particles supplied into a nozzle 1, in the direction indicated by an arrow A, are electrificated by corona ions which generate from corona electrodes 6 to which a high voltage is applied by means of high voltage source 5, when the powder particles pass through a conical gap between a diffuser member 3 fixed to a body 2 and a deflector 4 mounted on the nozzle member 1 at the right end thereof. In order to homogeneously disperse the powder particles and to form a uniform sprayed layer on a surface to be coated, narrow apertures 7 and an annular vortex chamber 8 are provided, so that the air supplied into the gun, as indicated by an arrow B, becomes a vortex air flow in the vortex chamber. In this gun, the nozzle member 1 and an annular member 9 defining the vortex chamber are made of brass. On the other hand, the other parts, indicated by hatchings, are made of any suitable resin material.
However, the conventionally known corona discharge spray gun mentioned above is known to have the following disadvantages.
1. The inner surfaces of the passages for the vortex air, especially the vortex chamber 8 into which the vortex air is discharged, tend to be easily worn away, thereby shortening the service life of the gun. In the case where the gun is continuously used, the service life thereof is usually one month. FIG. 4 is an enlarged view of the portion indicated by IV in FIG. 3, but illustrates the state of this portion after the gun has been used continuously for one month. Portions indicated by L.sub.1 and L.sub.2 of the annular chamber 8 which is defined by the nozzle member 1, the annular member 9 and the diffuser 3 are considerably worn away, and thereby the function of the vortex air generation is disturbed.
2. The spray powder particles adhere to the various portions of the gun and sometimes are dispersed in the state of lumps, which adhere to the surface to be coated, causing convex defects are formed on the sprayed surface. FIG. 5 is an enlarged view of a portion indicated by V in FIG. 3, but illustrates the state of this portion after the gun has been continuously used for four hours. The powder particles P have adhered to a step portion between the nozzle member 1 and the hose 10, thereby causing convex defects on the sprayed surface. FIG. 6 is an enlarged view of a portion indicated by VI in FIG. 3, but illustrates the state of this portion after the gun has been continuously used for four hours, wherein the powder particles P have adhered to the nozzle member 1 at the opposite side of the discharge ports 1a, thereby causing convex defects. FIG. 7 is an enlarged view of a portion indicated by VII in FIG. 3, but illustrates the state of this portion after the gun has been continuously used for four hours, wherein the powder particles also have adhered to the electrodes 6, thereby causing convex defects on the surface.